Electric insulator



March 3, 1942. J. J. TAYLOR ELECTRIC INSULATOR Filed July 11, 1940 FIG.

FIC-LZ INVENTOR BY J0 h n J.Taylor r/ ATTORNEY Patented Mar. 3, 1942ELECTRIC INSULATOR John J. Taylor, Wadsworth, Ohio, assignor to The OhioBrass Company, Mansfield, Ohio, 'a corporation of New Jersey ApplicationJuly 11, 1940, Serial No. 344,941

1 Claim.

This invention relates to electric insulators and particularly to meansfor reducing or preventing radio disturbance from insulators of thesuspension type. Heretofore insulators have been provided on theirsurface with semi-conducting coatings extending over the surfaces of theinsulators away from the metallic fittings to reduce or preventdisturbance caused by discharges from the fittings over the insulatorsurfaces, as disclosed in Patent 1,735,829, granted to A. 0. Austin,November 12, 1929, and assigned to The Ohio Brass Company of Mansfield,Ohio. Various forms of semi-conducting coatings have been employed inaddition to those disclosed in the Austin patent, one form beingdisclosed in the patent of Hawley, No. 1,668,123, and another in thepatent to Sleeman No. 2,154,387.

While the coatings disclosed in the prior patents reduce to some extentthe surface discharges and radio disturbances of electric insulators, O

applicant has found that the effectiveness of such coatings can begreatly improved, especially on suspension insulators, by shaping thedielectric member so as properly to dispose the terminal edge portionsof the coatings relative to each other and to the electrostatic fieldproduced in the dielectric medium and surrounding atmosphere.

After extensive investigation, applicant has found that theeffectiveness of the treatment depends, not so much upon the dispositionof the separate coatings per se as it does upon the relation of thecoatings on opposite sides of the dielectric member to each other and tothe dielectric.

One object of the present invention is to pro- 7 tion and arrangement ofparts shown in the accompanying drawing and described in the followingspecification and it is more particularly pointed out in the appendedclaim.

In the drawing:

Fig. 1 is an elevation partly in section of a a.

suspension insulator treated in accordance with the present invention.

Fig. 2 is a view similar to Fig. 1 showing a slightly different form oftreatment for producing the same result as that produced in Fig. 1.

In both figures the numeral l0 designates a dielectric member formingthe insulating body of a suspension insulator having a cap II and a pinl2 cemented thereto in the usual manner. Applied to the outer surface ofthe dielectric l0, adjacent the lower edge of the cap II, is a highresistance or semi-conducting coating [2. This coating is indicated inthe drawing by a heavy line and extends a suilicient distance beneaththe cap to make good electrical contact with the cement l3 and hencewith the cap H. At its lower edge the coating extends out along theupper surface of the dielectric member In for a distance ofapproximately an inch the width of the coated zone depending upon thesize of the insulator and the conditions under which it is to operate.

In the form of the invention shown in Fig. l, the inner surface of thepin hole is not shown as covered by a conducting coating but is providedwith a circumferential pocket l4 which is partially closed at its lowerside by an inwardly inclined lip 15 on the lower surface of thedielectric member H]. The cement l6 which holds the pin l2 within thepin hole extends downwardly in the pocket M a sufficient distance thatthe cement terminates on the downwardly and inwardly inclined uppersurface of the lip l5. Since the cement I6 is partially conducting theouter surface of the cement will have the potential of the pin l2 andthe points of greatest electrostatic stress will be located at the outeredge of the coating I2 and at the lower extremity of the contact of thecement I6 with the upper surface of the lip IS. The field of greatestelectrostatic stress will be set up between the outer edge of thecoating [2 and the terminal edge of the cement l6 and the lines of forceextending between these two edges will be almost entirely confined tothe dielectric member [0. Not only is this true, but these lines offorce in each case are directed backwardly away from the terminal edgeof the coated surface of the dielectric member, thus tending to restrainany discharge from these edges. This is not only true of the localelectrostatic field set up by the conducting members on opposite sidesof the dielectric flange but also true of the general electrostaticfield set up by the conductor and supporting structure for the insulatorstring. The high resistance of the conductor coating l2 and of thecement it also tends to prevent discharge from the terminal edges ofthese elements, particularly if the resistance of the coating I2 isgraded as suggested in the Austin patent cited above.

Of course, all of the electrostatic lines of force do not extenddirectly between the two terminal edges of the conducting members, butextend in curves of gradually increasing length at either side of thefield of greatest stress. However, with the form and arrangement shownin the drawing only the very weak portion of the field at its outerfringe approaches a direction tangent to the surfaces of the dielectricmember at the ter-- minal lines of the conductors, and only the lines offorce defining the very weak field extend into the surroundingatmosphere. This is due to the relation of the radially extendingcoating on the upper surface of the dielectric member to the terminaledge of the internal conductor on the inwardly and downwardly slopingsurface of the internal pocket. In actual operation this particularrelation has been found to give results far superior to all otherarrangements in which this relation is not maintained.

In some cases it may not be desirable for mechanical reasons to extendthe cement I 6 into the pocket 14 but where this is true, the desiredrelation of the electrodes and dielectric member may be secured byproviding the inner surface of the pocket 14 as shown in Fig. 2 with asemiconducting coating l1 similar to the coating l2. The distribution ofthe electrostatic field and the operation of the insulator in this casewill be similar to that produced by the arrangement shown in Fig. 1.

I claim:

In combination, a dielectric member having a radial flange, and having aboss on the upper side of said member and a recess extending into saidboss from the lower side of said member, a cap secured to said boss andterminating adjacent the surface of said flange, a pin secured withinsaid recess, a semi-conducting coating electrically connected with saidcap and extending over the upper surface of said flange away from saidcap and terminating on the radially extending portion of said surface,the wall of said recess being shaped to form a circumferential pocketwithin said recess and adjacent the mouth thereof, said pocket beingpartially closed at its lower side by a downwardly and inwardlyextending lip on the lower side of said dielectric member, andconducting means on the inner surface of said recess and pocketterminating within said pocket, the terminal edge of the portion of theinner surface of said recess in contact with said conducting means beingdirected inwardly toward the axis of said insulator while the terminaledge of the semi-conducting coating on the upper surface of the flangeis directed outwardly away from the axis of the insulator so thatelectrostatic lines of force connecting the terminal edges of theconducting means on the opposite surfaces of said dielectric member willbe contained chiefly within the body of said dielectric member and willbe directed away from the terminal edges of the conducting means on saidsurfaces.

J OHN J. TAYLOR.

